Blender Doesn't Permit Indices in Drivers?
As I said in the comments

Raising a value to a power is pretty standard math, something python can defiantly do.

Your trouble comes from a simple python syntax error. You are using ^ when the syntax in python is  ** for power of (^ is the bitwise XOR operator
).  As you can see here in the python docs ** is the the correct form.

You could alternatively use pow() function.